ABSTRACT: In space, muscles atrophy due to the lack of a gravity vector against which to do work. Traditional exercise devices intended for use in microgravity, such as rubber bands and bungee cords, fail to provide measurable constant quantitative forces on the muscles that are necessary for optimal muscle maintenance. Furthermore, research indicates that because loaded eccentric (ECC) contractions occur during normal daily activity but are absent in microgravity, an exercise countermeasure device that could provide an increased ECC load during exercise would be ideal to combat microgravity-induced muscle atrophy.

Our proposed KC-135 experiment investigates muscle responses in microgravity during common muscle strengthening routines while exercising with our unique Constant Force Resistive Exercise Unit (CFREU). The CFREU is a gravity-independent exercise unit designed to provide resistive forces on the muscles at a constant force both concentrically and eccentrically. To meet the need for increased ECC loading in microgravity, we have incorporated designs into the CFREU that will provide increased ECC loading on the muscles during exercise. To investigate the physiological feasibility of the CFREU design for use in microgravity, non-invasive surface electromyography (sEMG) will obtain muscle activity response during exercise on a KC-135 flight using a series of different ECC:CON ratios. We hypothesize that sEMG muscle activity responses during exercise with the CFREU on the microgravity-based portions of the KC-135 will reflect muscle activity comparable to ground-based sEMG data collected during exercise with a standard isokintetic dynamometer, which is a machine capable of providing various ECC:CON loading ratios during rehabilitative exercise.